Effects of radiation directivity of extended sources of large earthquakes have been known to seismologists for a long time, but only in recent decades, with the development of dense networks of seismic observations, representative materials appeared and the possibility for a detailed study of these effects.

Since the 2000s, seismologists have been finding evidence of fast super-shear crack propagation along the fault planes, leading to the formation of shock fronts (Mach cones) due to the interference of seismic waves radiated by the propagating crack tips; and high peak ground accelerations (PGA) and peak ground velocities (PGV) were recorded in near-fault zones.

In such cases, serious damage occurred in near-fault zones associated with the impacts on buildings of high-amplitude velocity pulses (at components parallel to the fault), followed by another type of the impacts, from rupturing with sub-Rayleigh velocities, with the dominance of components normal to the fault. The double-impact effects destroyed structures. Such phenomena were observed during the 2023 Turkish earthquakes. Other examples of such kind of earthquakes are 2016 Kumamoto earthquakes in Japan.

Since the late 1990s, seismologists are trying to include the effects of radiation directivity of extended earthquake sources to the procedures of probabilistic seismic hazard analysis (PSHA) and to building codes, but to date, no consensus has been reached, and the progress in this area can be expected only with the accumulation of sufficient observational data.

Experimentally observed effects of anomalously weak and strong amplification of seismic waves in soft subsurface soils are studied using the records of KiK-net seismic vertical arrays (of strong motion network of Japan). The amplification was estimated based on peak ground accelerations recorded during ~20 earthquakes at each station. To interpret the obtained results, we engaged models of soil behavior at these sites during the Tohoku earthquake on March 11, 2011.

With this work, we start studying of the response of soils of various types (among 11 types of the most representative surface soils on the territory of Russian Federation) in seismic motion, based on in situ observations (KiK-net data). The response of soft sandy and loess soils to weak and medium-intensity seismic motion is analyzed. We show that the response of rather homogeneous soil profiles (without clear seismic boundaries) to seismic motion is frequency-dependent and contains resonant frequencies, at which seismic motion is noticeably enhanced. At stronger seismic motion, the resonant frequencies are reduced, and the amplification of seismic motion by soil layers is also reduced. These effects are not taken into account in seismic rigidity method, the application of which is still required by the Building codes acting in Russia. We should change the practice of application of the seismic rigidity method in the Building codes, by clearly defining the scope of the method, and we should move to the spectral description of the corrections for ground conditions in earthquake resistant construction, by means of response spectra, as done in other countries.

Renovated Russian building codes SP 14.13330.2014 “Construction in seismic areas” in sections concerning seismic loadings and soil conditions are discussed.

The updated SP did not change much compared to the previous version SNiP II-7-81*, and the response spectra are simplified. The updated documents do not take into account new knowledge on the manifestations of seismicity, soil behavior during strong earthquakes, and spatial distribution of soils over the territory of Russia, they keep outdated provisions that have already shown their insolvency. The application of one seismic zonation map in the calculations for “project earthquake” and for “maximum credible earthquake” (PZ and MRZ) contradicts to the logic of probabilistic seismic zonation maps OSR-97.

To make the updated SP the documents of a modern scientific level, we should introduce significant changes in them, concerning soil classification, selection of “base” soil type, accounting for soil conditions, application of the method of seismic rigidities (VSZ), and the use of seismic zonation maps OSR-97 for the calculations on PZ and MRZ.

At present within the framework of the Federal Target Program (FTP) «Increasing resistance of dwelling houses, basic life-supporting facilities and systems in seismic areas of the Russian Federation for 2009-2014», the Design Research Institute of Engineering Surveys in Construction (OAO PNIIIS) in cooperation with specialists from the Institute of Physics of the Earth of the Russian Academy of Sciences, carries out updating of seismic zoning maps of the Russian Federation territory. Due to the importance of the country’s seismic zoning, this work needs detailed and comprehensive discussion. This paper deals with scientific discussion of this work results.
It is shown that in making the OSR-97* and OSR-2012 maps, the earthquake engineering data on the regional parameters of seismic wave radiation and propagation on Russia’s territory, being necessary for calculations, were not used. This information is virtually unavailable:  OSR-97* and OSR-2012 maps, as well as previous OSR-97 maps, only one value of quality factor Q~150 at frequency f = 1 Hz is used for the vast territory of Russia, together with the relationships between seismic intensity and peak ground accelerations, obtained for California (USA) - the region with its own features, which are not typical for Russia. All this leads to substantial errors, especially, in mapping under peak ground accelerations.

Updated accurate estimates of seismic effects from scenario earthquakes are obtained for the areas of Kolsky peninsula and Karelia; calculations were carried out with regional characteristics of radiation and propagation of seismic waves that were estimated based on records of local earthquakes. Seismic intensity, peak ground accelerations and velocities, response spectra, and other characteristics are estimated from acceleration time histories of motions on the surface calculated by stochastic method. Higher estimates of seismic intensity and peak ground accelerations and velocities were obtained, as compared to the estimates obtained earlier and based on world-average characteristics or from areas with similar geological structure. The main cause of the obtained differences and high new estimates of seismic effects is neglecting in past studies high values of the stress drop, ??~bars, typical for this region.

The normative formulas of SP 286.1325800.2016 for estimation of peak ground accelerations in earthquakes were checked on records obtained in the near-fault zones of strong earthquakes (MS ~6.9÷7.15) of Japan made by K-NET and KiK-net stations. It was found that the recorded values of peak accelerations have a fairly large scattering even in the selected narrow range of magnitudes, which is obviously due to local site effects (soil response, topographic effects, etc.), as well as to differences in the characteristics of the earthquake sources and the paths of seismic wave propagation. Calculations by the normative formulas produced estimates that are near the lower limit of the recorded peak accelerations, and in the near-source zones, they noticeably underestimate the recorded peak accelerations. In general, the formulas of SP 286.1325800.2016 give us only approximate estimates, and therefore, it is necessary to develop more reliable methods for estimating peak accelerations and other parameters of seismic motion, taking into account soil conditions and regional characteristics, with components of probabilistic analysis.